1. Field of the Invention
The present invention relates to a multi-wavelength channel transmission-type optical filter and more particularly, to the multi-wavelength channel transmission-type optical filter which is capable of more narrowing the width of the wavelength in an optical filter by employing Mach-Zehnder interferometer having a function of generating and dividing the multi-wavelength channel signals in an large capacity of wavelength division multiplexing optical communication.
2. Description of the Related Art
Generally, in the large capacity of wavelength division multiplexing optical communication, it is necessary to stabilize and standardize a wavelength of multi-wavelength channel and also it is important to ensure an element which is capable of dividing the multi-wavelength channel signal. In order to divide several channel signals in an optical communication through the multi-wavelength channel, a method can be implemented for using a plurality of the conventional single wavelength optical filters. However, this method is not suitable to constitute a good system because the more the number of channel to be divided becomes increased, the more the strength of light becomes weak, and also the volume of light becomes large.
There is an interferometer-type optical filter (disclosed in Electronics Letter, vol. 30, pp.642-643, 1994) for using an arrayed-waveguide grating (AWG) as an optical filter that is capable of dividing the multi-wavelength channel, simultaneously. This filter has become much developed recently, but fabrication is complex and it is not easy to control the gap of transmission wavelength (or, frequency) and the width of wavelength(.DELTA..lambda.)(or .DELTA.v). Compared to it, a Mach Zehnder interferometer type optic filter has an advantage that is capable of controlling easily the transmission wavelength and that its fabrication is also very simple. However, the bandwidth of the transmission wavelengths becomes wide comparatively because the wavelength to be transmitted is transmitted sinusoidal depending on the output of the interferometer.